Variable pitch fan for heat exchangers

ABSTRACT

The fan includes a hub assembly with a plurality of radially extending fan blade holders. A blade is mounted in each blade holder for rotation around its longitudinal axis to vary its pitch. A crank is connected to each blade to rotate the blade relative to the holder. A crank rod extends between each crank so the rotation of one crank will be imparted to all the other cranks. Jack screws located on opposite sides of the hub assembly rotate the crank arms when the pitch of the blades is to be changed and hold the crank arms from further rotation when the blades have the desired pitch angle.

United States Patent 151 3,684,398 Davidson et al. 451 Aug. 15, 1972 [54] VARIABLE PITCH FAN FOR HEAT 1,915,465 6/1933 Kohlstedt ..41/155 EXCHANGERS [72] I t E M Da dso R be" C FOREIGN PATENTS OR APPLICATIONS s: men or both fl 'g 3 1,063,324 13/1959 Germany ..416/155 [73] Assignee: Hudson Products I Corporation, Primary Examiner-Everette A. Powell, Jr.

Houston, Tex. Attomey-l-Iyer, Eickenroht, Thompson & Turner [22] F1led: April 24, 1970 ABSTRACT [21] Appl' 15643 The fan includes a hub assembly with a plurality of radially extending fan blade holders. A blade is [52] 0.8. CI ..416/155, 416/168 mounted in each blade holder for rotation around its [51] Int. Cl ..F04d 29/36 longitudinal a i o ary i s pitch- A crank is con- [58] Field of Search ..416/155, 158, 168, 159, 166, nected to each blade to rotate the blade relative to the 4 147 holder. A crank rod extends between each crank so the rotation of one crank will be imparted to all the 6 f other cranks. Jack screws located on opposite sides of [5 1 Re erences CI ed the hub assembly rotate the crank arms when the UNITED STATES PATENTS pitch of the blades is to be changed and hold the 1,780,431 11/1930 McCarrolL; ..416/155X ggg fgg ggg f fijg g when the blades 3,467,198 9/1969 Ellinger ..416/157 X 1,793,652 2/1931 Tumbull ..416/155 1 Claim, 4 Drawing Figures PATENTEDAIJI; 15 I972 saw 1 or 2 FIG] 0 O S M V G D M e n e Q U E Robert C. Monro INVEN TORS r, a W

EVA 7p ATTORNEVS PATENTEnms 15 I972 SHEET 2 OF 2 Eugene M. Davidson Robert C Monroe /N VE N TORS ATTORNEYS VARIABLE PITCH FAN FOR HEAT EXCHANGERS This invention relates to improvements in variable pitch fan assemblies and in particular to such fan assemblies that are used in heat exchangers.

This invention has particular utility in connection with relatively large air cooled heat exchangers where cooling water is circulated through tube bundles across which air is drawn by the fans. Preferably, the outlet temperature of the water is maintained substantially constant. To do this it is necessary to vary the volume of air flowing by the tubes as the ambient temperature of the air varies. This is done by changing the pitch of the fan blades. In climates where the-ambient temperature may be quite cold during the winter months, it may be necessary to place the blades in negative pitch to reverse the flow of air to get the cooling required without also freezing the water in the tubes. Under such conditions, should there be a power failure in the pitch control system, it is imperative that the pitch of the blades remain fixed in the last set pitch angle, for if they do not, the cooling rate may rapidly increase causing the water to freeze and burst the tube bundles.

Therefore, it is an object of this invention to provide a fan blade assembly for heat exchangers wherein the pitch of the blades will not change, but remain at the last setting even though there be a failure in the power supply for the pitch control system.

It is a further object of this invention to provide a fan blade assembly in which the pitch of the blades is controlled through a drive mechanism that is irreversible and will hold the blades in their last set pitch angle should the power supplied to the pitch control means fail.

It is an additional object of this invention to provide a fan blade assembly in which the pitch of the fan bladesis changed through a jack screw assembly that will hold the blades at the last set pitch even though there is a failure in the power supplied to the jack screw.

These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached drawings and appended claims.

The invention will now be described in detail in con-' nection with the attached drawings in which,

FIG. 1 is a top plan view of the preferred embodiment of the fan blade assembly of this invention;

FIG. 2 is a view of the assembly in FIG. 1 looking in the direction of arrows 22;

FIG. 3 is a cross section through one of the blade holders of the hub assembly; and

FIG. 4 is a view taken along line 44 of FIG. 3.

The fan blade assembly includes hub assembly and a plurality of fan blades l2a-l2h. The hub assembly includes central hub 14 and a plurality of radially extending blade holders 16a-l6h. Central hub 14 is mounted for rotation around central axis 140 that is perpendicular to the apparatus, as viewed in FIG. 1. The apparatus for doing this are not shown in the drawings since they form no part of this invention.

Each fan blade is mounted in its blade holder for rotation around its longitudinal axis. Since in the embodiment shown all blades are mounted in the same manner in the blade holders, only one blade holder/fan blade assembly will be described in detail. For this purpose, FIGS. 2, 3, and 4 are directed to the assemblyof blade 12c and blade holder 16:.

Referring first to FIGS. 3 and 4, blade holder includes support member 18, which extends radially outward from hub 14. lntegrally connected to the outer end of member 18 is tubular bearing housing 20. Means are provided for supporting a fan blade in each blade holder for rotation around the longitudinal axisof the blade so that the pitch angle of the blade can be changed. In the embodiment shown, said means includes clamp 24 and shaft 26. Circular shank 22 of blade 12c is positioned in clamp 24. The clamp has upper portion 24a and cap 24b which are bolted together to anchor the blade in the clamp. Tubular shaft member 26 is integrally connected to upper portion 24a of the clamp. Bearings 28 and 30 are posi' tioned adjacent each end of bearing housing 20 to support shaft 26 for rotation around its longitudinal axis, which coincides with the longitudinal axis of blade 12c.

A plurality of crank arms 32a-2Ih are provided to transmit torque to the blades for rotation around their longitudinal axis. One end of each crank is attached to its associated blade mounting means. As shown in FIG. 3, crank 320 has one end attached to the end of shaft 26 through cap screws 34. Thus, rotation of crank 32 will rotate shaft 26 and blade 12c around their longitudinal axes and change the pitch angle of the fan blade.

Means are provided to move all of the blades through the same pitch angle when one blade is rotated and to hold the blades against independent axial rotation. In the embodiment shown, crank control rods 36a-36h are connected between the free ends of adjacent cranks so that movement of one crank will be imparted to all of the other cranks.

Means are provided for rotating at least one of the cranks to move the fan blade to which it is attached to the desired pitch angle and, through the crank control rods, to rotate each crank in the same direction and through the same angle to keep each fan blade at the same pitch angle. In the embodiment shown jack screws 40 and 50 are provided for this purpose. Both are arranged in the same manner with respect to the cranks they move so only jack screw 40 will be described in detail. As shown in FIG. 4, jack screw 40 has its upper end 40a connected through pin 41 and arm 42 to bearing housing 20 of the blade holder. Arm 42 is rigidly connected to the blade holder so that end 40a of the jack screw is fixed relative thereto. The other end 40b of the jack screw is connected by pin 43 to crank 32c. Pins 41 and 43 allow pivotal movement between the ends of the jack screw and the members to which they are connected.

The jack screw includes gear housing 44 in which is located bevel gear 44a and worm gear 44b (both shown dotted in the drawing). Bevel gear 44a is connected to lead screw 45 of the jack screw so that rotation of the gear will cause rotation of the lead screw. The other portion of the jack screw comprises nut assembly 46 which includes a female threaded section that engages the threads on lead screw 45 so that rotation of the lead screw will cause the nut assembly to move toward and away from gear housing 44.

As shown in FIG. 4, rotation of the lead screw to move the nut assembly toward the gear housing will impart clockwise rotation to crank 32c and in turn to fan blade 12c. Rotation of the lead screw in the other direction will cause counterclockwise rotation of the crank and the fan blade to which it is connected. As crank 320 is so moved, it will impart the same movement mall the other cranks of the fan blade assembly through the crank control rods.

The angle through which the blades can be moved is limited. In the embodiment shown, cap screws 47 and 48 are located in tapped holes in the crank assembly and positioned to engage portions of support member 18 of fan blade holder 16c and limit the angle through which the crankcan be rotated. This distance can be adjusted to some extent by adjusting the position of the cap screws in their tapped holes.

As said above, in the embodiment shown two jack screw assemblies are employed. The one just described, jack screw assembly 40, is arranged to rotate crank 32c. Jack screw assembly 50 is located diametrically opposite crank 320 to impart similar rotation to crank 323. Two jack screws are used to insure a smoother movement being imparted to all the cranks. Also, the two are placed on opposite sides so each crank will be pulling on one-half the control rods and tend to keep them in tension rather than compression.

The means for moving the cranks includes a source of power for operating the jack screws. In the embodiment shown, electric motor 52 is mounted on hub 14 with its longitudinal axis coinciding with axis 140, the axis of rotation of the hub. Electric motor 52 drives the jack screws through'transmission 54 and torque rods 56 and 58. The torque rods transmit rotation from the electric motor to the gear boxes of the respective jack screws to cause rotation of the fan blades to the desired pitch angle.

l The invention having been described, what is claimed is:

l. A fan blade assembly for heat exchangers, comprising a hub rotatable about a central axis and having at least four blade holders extending radially therefrom in generally equally spaced apart relation, a motor on the hub, blades having their inner ends supported by the holders for rotation about their longitudinal axes, first and second torque rods having their inner ends connected to the motor for rotation and extending outwardly to a position in which their outer ends are near the inner ends of first and second blades, respectively,

' first and second jack screws having their opposite ends pivotally connected to said first and second blades and the holders for said first and second blades, respectively, means'connecting the outer ends of the first and second torque rods to intermediate portions of the first and second jack screws, respectively, for rotating the first and second blades in their holders in response to rotation of said first and second torque rods, and control rods pivotally connecting the inner end of each blade with the inner end of each of two other blades, the pivotal connection of said control rods to said first and second blades being removed from the pivotal connection thereto of said first and second jack screws, so as to provide means for imparting rotation to said first and second blades independently of the jack screws connected thereto. 

1. A fan blade assembly for heat exchangers, comprising a hub rotatable about a central axis and having at least four blade holders extending radially therefrom in generally equally spaced apart relation, a motor on the hub, blades having their inner ends supported by the holders for rotation about their longitudinal axes, first and second torque rods having their inner ends connected to the motor for rotation and extending outwardly to a position in which their outer ends are near the inner ends of first and second blades, respectively, first and second jack screws having their opposite ends pivotally connected to said first and second blades and the holders for said first and second blades, respectively, means connecting the outer ends of the first and second torque rods to intermediate portions of the first and second jack screws, respectively, for rotating the first and second blades in their holders in response to rotation of said first and second torque rods, and control rods pivotally connecting the inner end of each blade with the inner end of each of two other blades, the pivotal connection of said control rods to said first and second blades being removed from the pivotal connection thereto of said first and second jack screws, so as to provide means for imparting rotation to said first and second blades independently of the jack screws connected thereto. 